1. Field of the Invention
The invention relates to apparatus for generating information regarding the presence and size of an occupant seated within a motor vehicle.
2. Background Art
It is increasingly desirable to tailor the response of a vehicle passenger safety restraint to a detected presence and size of a vehicle occupant. One known expedient is to obtain a measure representative of a weight placed upon the seating surface of an occupant""s seat. Because the prior art has sought to provide a weight-sensing capability with little or no alteration of the seat""s supporting structure, the prior art teaches providing a measure representative of both the presence and the weight of an object placed on a vehicle seat using a plurality of strain gage sensors bonded to a structural support for the seat.
Under a first known approach, the strain gage sensors are attached to the risers with which the seat""s supporting platform, such as a track assembly permitting relative longitudinal movement of the seat within the vehicle, is secured to the vehicle floor. This approach advantageously requires only minimal alteration to the design of the track assembly risers. Unfortunately, because a relative movement of the track assembly""s upper and lower rails will effect a change in the loads exerted on the individual risers in response to a given weight placed on the seat, this approach requires the detection of the relative longitudinal position of the upper rail relative to the lower rail, and relatively complex algorithms with which to obtain an estimate of occupant weight based upon strain gage and position sensor outputs. The estimation of occupant weight is further complicated by the overhanging loads that are likely to be placed on one or more of the risers, due to typical seat and track assembly geometries.
Under another known approach, U.S. Pat. No. 6,039,344 teaches a vehicle occupant weight sensor apparatus wherein the seat pan of a vehicle seat frame is coupled to an upper rail of a seat track assembly by a plurality of elongate sensing beams, with each sensing beam including a plurality of strain gages connected to an appropriate Wheatstone bridge. Typically, such prior art occupant weight sensing systems rely upon joint rotation at the joints formed at each end of the beam in order to generate the desired response from the system""s strain gages. Indeed, U.S. Pat. No. 6,231,076 teaches the use of a sensor assembly that employs a bent metal substrate designed to maximize sensing element flexure through joint rotation. Unfortunately, complex algorithms are similarly required to obtain an estimate of occupant weight from the resulting stain gage output because the algorithm must account for the moments exerted on the stain gage substrate at the joints due to the resilient flexing of the seat""s structural supports. Such apparatus are still likely to incur a loss of desired weight-sensing resolution as a result of such joint rotation.
It is an object of the invention to provide a weight-sensing assembly for supporting a seat cushion frame, as may form the structural foundation for a seat of a motor vehicle, that avoids the computational complexities resulting from rotation at the joints formed between the seat""s structural supports and a weight-sensing element of the assembly.
It is also an object of the invention to provide a weight-sensing assembly for supporting a seat cushion frame of a motor vehicle atop a floor-mounted track assembly that features an improved weight-sensing resolution over known assemblies.
A further object of the invention is to provide a weight-sensing assembly for supporting a seat cushion frame within a motor vehicle that requires minimal alteration to the design of either the frame or the platform upon which the frame is to be mounted.
Under the invention, a weight-sensing assembly is provided for supporting a seat cushion frame having a plurality of spaced mounting locations above a platform that likewise includes a plurality of spaced mounting locations in general opposition to the mounting locations of the frame. The assembly includes one or, preferably, two elongate coupling members, each of which includes a first and second set of spaced mounting locations, for example, proximate to each longitudinal end thereof, such that the first set of mounting locations of a given coupling member is generally aligned with and secured to the mounting locations of a first one of the frame and the platform. The second set of mounting locations of each given coupling member is generally laterally offset from the mounting locations of a second one of the frame and the platform.
Thus, in an exemplary weight-sensing assembly constructed in accordance with the invention, each coupling member is secured at its respective first set of mounting locations to the aligned mounting locations defined on the seat cushion frame. In this exemplary embodiment, the coupling members"" second set of mounting locations are laterally offset from the mounting locations defined on an upper surface of a track assembly that otherwise accommodates generally longitudinal translation of the seat cushion frame within the motor vehicle in a known manner. Preferably, where the exemplary weight-sensing assembly employs a pair of coupling members, the coupling members extend in a direction generally parallel to the upper tracks of the track assembly.
The assembly further includes a pair of sensors secured to each coupling member. Each sensor includes an elongate sensing beam having a longitudinal axis extending between a first end and a second end, and at least one strain gage mounted on the sensing beam for generating an output signal representative of an elastic deformation of the sensing beam in a bending plane that includes the longitudinal axis of the sensor. Preferably, the at least one strain gage is mounted proximate to the longitudinal midpoint of the sensing beam, and the sensing beam of each sensor is preferably of generally uniform cross-section. The strain gages are connected in electrical communication with an electrical bridge circuit, with which to generating a signal representative of a weight placed on the seat cushion frame.
The first end of the sensing of each sensor is secured to a respective mounting location of the second set of a given coupling member""s mounting locations to form a first joint proximate to each longitudinal end of the given coupling member. The second end of the sensing beam of each sensor is secured to a respective one of the mounting locations of the second one of the frame and the platform to form a second joint. Thus, in the exemplary embodiment wherein the first set of mounting locations on each coupling member is secured to the seat cushion frame, the second end of each sensing beam is secured to a respective mounting location defined on the upper surface of the track assembly.
Under the invention, the sensing beam of each sensor, the coupling member, and the second one of the frame and the platform each have a respective flexural stiffness resisting bending in a bending plane that includes the longitudinal axis of the sensing beam of at least one of the sensors. The respective flexural stiffness of the coupling member and of the second one of the frame and the platform is at least about three times greater than the flexural stiffness of the sensing beam of each sensor. As a result, a displacement of the coupling member relative to the second one of the frame and the platform in response to a weight placed on the frame is characterized by a negligible joint rotation, such that . Most preferably, the respective flexural stiffness of the coupling member and of the second one of the frame and the platform is at least about five time greater than the flexural stiffness of each sensor""s sensing beam.
In accordance with another feature of the invention, in order to further improve the assembly""s resolution, i.e., its ability to detect small changes in weight placed atop the seat cushion frame, each coupling member includes an elongate portion of generally uniform cross-section separating at least the second set of mounting locations. Most preferably, the elongate portion of the coupling member has a neutral surface in response to bending in the bending plane that is generally coplanar with the neutral axis in bending of the sensing beams of the attached sensors. The elongate portion of each coupling member further preferably includes a plane of symmetry in response to bending in the bending plane, with the sensing beam of at least one sensor having as a plane of symmetry in response to bending in the bending plane that is generally coplanar with the plane of symmetry of its respective coupling member.
From the foregoing, it will be appreciated that the invention, by avoiding joint rotation and driving the weight-induced stresses in the sensing beams of the sensors to each beam""s center, advantageously provides a weight-sensing assembly for supporting a seat cushion frame atop a supporting platform, such as a seat track assembly of a motor vehicle, whose strain gage output provides increased resolution while being less susceptible to change in response to a change in the longitudinal position of the seat cushion frame relative to the platform""s supporting risers. And, because the invention""s weight-sensing assembly includes the strain gage sensors, the weight invention can beneficially be integrated into existing vehicle seating designs with minimal alteration to either the seat cushion frame or the supporting platform.
Other advantages, features, and benefits of the invention will be readily apparent from the following detailed description of a preferred embodiment, when taken in connection with the accompanying Drawings.